[ArrogantBustard]

For some reason, I am reminded of my absolute, all-time favourite engineering study:

A Stress Analysis of a Strapless Evening Gown

Click the "PDF" button for the complete text of the study.

[Nonstatist]

Reading over the paper, in summary, one can say the saggier the breast, the smaller the cup will be required in order to increase the local normal forces there and hence, to increase the vertical friction forces needed to balance the weight of the "endownment" .

Or, to put it another way, unless youre young and "perky", wearing a strapless dress is going to be mighty uncomfortable!!